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                    结构化分析概述
            
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        <a href="." >结构化分析概述</a>
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                                <h1 id="软件工程导论">软件工程导论</h1>
<h2 id="结构化分析概述">结构化分析概述</h2>
<h3 id="核心思想">核心思想</h3>
<blockquote>
<p>面向数据流需求分析方法</p>
</blockquote>
<ul>
<li>分解化简问题</li>
<li>物理与逻辑表示分开 <blockquote>
<p>逻辑：是什么，做什么；物理：怎么做，实现细节</p>
</blockquote>
</li>
<li><p>进行数据与逻辑抽象</p>
<h3 id="结构化分析具体步骤">结构化分析具体步骤</h3>
</li>
<li>发现需求</li>
<li>求精-对发现需求反复求精多次细化</li>
<li>建模<ul>
<li>模型核心：数据字典-软件使用和产生的所有所有数据对象</li>
<li>数据模型：E-R图-数据对象间的关系</li>
<li>功能模型：DFD图(数据流图)-数据在软件中移动、变换及相应功能</li>
<li>行为模型：状态转换图-描述系统状态和不同状态之间的转换方式<blockquote>
<p>结构化分析有三大模型：数据模型、功能模型、行为模型</p>
</blockquote>
</li>
</ul>
</li>
<li>规格说明 <blockquote>
<p>书写软件需求规格说明书，这是测试的标准，也是用户验收的标准</p>
</blockquote>
</li>
<li>复审</li>
</ul>
<h3 id="数据模型">数据模型</h3>
<blockquote>
<p>数据模型由数据对象，数据对象之间的关系，属性组成</p>
</blockquote>
<ol>
<li>数据对象：软件必须理解的复合信息的表示；例如事务(报表)，地点(仓库)，角色(教师,学生)</li>
<li>属性：定义数据对象的性质；例如数据对象学生的属性可为：学号、姓名、班级等</li>
<li><p>关系：数据对象之间的关系；比如教师和学生之间存在“教”的关系。有1：1,1：n,m:n</p>
<h4 id="数据模型用【实体-关系图】表示：">数据模型用【实体-关系图】表示：</h4>
<ul>
<li>实体用矩形框</li>
<li>属性用圆角矩形</li>
<li>关系用菱形
<img src="static/images/实体-关系图.png" alt="实体-关系图图片"></li>
</ul>
<p><img src="static/images/E_R图.png" alt="E-R图图片">
E-R图可以转换成数据库中的数据表</p>
<p><img src="static/images/仓库管理系统ER图.png" alt="仓库管理系统ER图"></p>
<h4 id="功能模型">功能模型</h4>
<h5 id="数据流图">数据流图</h5>
<blockquote>
<p>数据流图(DFD)描绘系统逻辑模型，图中没具体的物理元素，只描绘信息在系统中的流动处理情况。</p>
</blockquote>
<ol>
<li>数据流图符号</li>
<li>正方形或者立方体：数据的源点或终点（人员，部门，计算机外部设备或传感器）</li>
<li>圆角矩形或者圆形：变换数据的处理（一系列程序、单个程序或程序的一个模块；人工处理过程）</li>
<li>开口矩形或者平行线：数据存储（文件，文件一部分，数据库元素，磁盘，磁带）</li>
<li>箭头：数据流，即特定数据的流动方向</li>
</ol>
<p><img src="static/images/一个简单的数据流图.png" alt="数据流图">
<img src="static/images/数据流图附加符号.png" alt="更多数据流图符号">
<strong>画数据流图并不是一下子就能画出来，而是先画源点、终点和数据处理整体，后边再一步步细化,注意数据流图只表示做什么，并不需要表示怎么做！</strong></p>
<p>一个完整的数据流图：
<img src="static/images/完整的数据流图.png" alt="完整的数据流图"></p>
<p>了解一下分层数据流图</p>
<h4 id="数据流图中的命名规范：">数据流图中的命名规范：</h4>
<p><img src="static/images/数据流图中的命名规范1.png" alt="数据流图中的命名规范">
<img src="static/images/数据流图中的命名规范2.png" alt="数据流图中的命名规范">
<img src="static/images/数据流图中的命名规范3.png" alt="数据流图中的命名规范"></p>
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